fix: various

internal/modules/system/locale.go

@@ -16,6 +16,7 @@ import (
 
 type LocaleStatusBody struct {
 	Lang      string `json:"lang" example:"it_IT.UTF-8" doc:"System locale (LANG)"`
+	Language  string `json:"language" example:"en_US:" doc:"Fallback language list (LANGUAGE)"`
 	VCKeymap  string `json:"vc_keymap" example:"it" doc:"Virtual console keymap"`
 	X11Layout string `json:"x11_layout" example:"it" doc:"X11 keyboard layout"`
 }
@@ -31,12 +32,14 @@ type LocalesOutput struct {
 type KeymapsOutput struct {
 	Body struct {
 		Keymaps []string `json:"keymaps" doc:"Available virtual console keymaps"`
+		Reason  string   `json:"reason,omitempty" doc:"When keymaps is empty, why: e.g. \"kbd not installed on this server\""`
 	}
 }
 
 type SetLocaleInput struct {
 	Body struct {
 		Lang     string  `json:"lang" example:"it_IT.UTF-8" doc:"Locale to set as LANG"`
+		Language *string `json:"language,omitempty" example:"en_US:" doc:"Fallback language list (LANGUAGE)"`
 	}
 }
 
@@ -56,6 +59,10 @@ type GenerateLocaleInput struct {
 // .charmap suffix (e.g. fr_FR, fr_FR.UTF-8, en_US.ISO-8859-1).
 var localeRe = regexp.MustCompile(`^[a-z]{2,3}_[A-Z]{2}(\.[A-Za-z0-9_-]+)?$`)
 
+// languageRe validates the LANGUAGE fallback list: colon-separated locale names
+// like "en_US:de_DE". Anchored so a leading "-" can't survive into argv.
+var languageRe = regexp.MustCompile(`^[a-zA-Z0-9_.:-]*$`)
+
 func localeStatus() (LocaleStatusBody, error) {
 	lines, err := oscmd.RunLines("localectl", "status")
 	if err != nil {
@@ -63,21 +70,28 @@ func localeStatus() (LocaleStatusBody, error) {
 	}
 	var b LocaleStatusBody
 	for _, line := range lines {
-		label, val, ok := strings.Cut(line, ":")
-		if !ok {
+		trimmed := strings.TrimSpace(line)
+		if strings.HasPrefix(trimmed, "VC Keymap:") {
+			b.VCKeymap = strings.TrimSpace(strings.TrimPrefix(trimmed, "VC Keymap:"))
 			continue
 		}
-		switch strings.TrimSpace(label) {
-		case "System Locale":
-			for kv := range strings.FieldsSeq(val) {
-				if k, v, ok := strings.Cut(kv, "="); ok && k == "LANG" {
+		if strings.HasPrefix(trimmed, "X11 Layout:") {
+			b.X11Layout = strings.TrimSpace(strings.TrimPrefix(trimmed, "X11 Layout:"))
+			continue
+		}
+		// Parse k=v fields on any other line (like System Locale block).
+		parts := strings.Fields(trimmed)
+		for _, part := range parts {
+			part = strings.TrimPrefix(part, "System Locale:")
+			part = strings.TrimSpace(part)
+			if k, v, ok := strings.Cut(part, "="); ok {
+				switch k {
+				case "LANG":
 					b.Lang = v
+				case "LANGUAGE":
+					b.Language = v
 				}
 			}
-		case "VC Keymap":
-			b.VCKeymap = strings.TrimSpace(val)
-		case "X11 Layout":
-			b.X11Layout = strings.TrimSpace(val)
 		}
 	}
 	return b, nil
@@ -144,7 +158,17 @@ func registerLocale(api huma.API) {
 		if !slices.Contains(locales, lang) {
 			return nil, huma.Error400BadRequest("unknown locale: " + lang)
 		}
-		if _, err := oscmd.Run("localectl", "set-locale", "LANG="+lang); err != nil {
+
+		args := []string{"set-locale", "LANG=" + lang}
+		if in.Body.Language != nil {
+			langVal := strings.TrimSpace(*in.Body.Language)
+			if !languageRe.MatchString(langVal) {
+				return nil, huma.Error400BadRequest("invalid language format: " + langVal)
+			}
+			args = append(args, "LANGUAGE="+langVal)
+		}
+
+		if _, err := oscmd.Run("localectl", args...); err != nil {
 			return nil, huma.Error500InternalServerError("set-locale failed", err)
 		}
 		return oscmd.OK(), nil
@@ -161,12 +185,14 @@ func registerLocale(api huma.API) {
 		Errors:      readErrors,
 	}, func(ctx context.Context, _ *struct{}) (*KeymapsOutput, error) {
 		// ponytail: minimal servers ship without kbd / /usr/share/keymaps, so
-		// localectl errors instead of returning empty. Treat that as "no keymaps
-		// available" rather than a server fault — set-keymap stays unreachable
-		// because nothing will be in the allowlist.
-		keymaps, _ := oscmd.RunLines("localectl", "list-keymaps")
+		// localectl errors instead of returning empty. Surface that as a `reason`
+		// the frontend can display ("kbd not installed") instead of an opaque N/A.
+		keymaps, err := oscmd.RunLines("localectl", "list-keymaps")
 		out := &KeymapsOutput{}
 		out.Body.Keymaps = keymaps
+		if err != nil || len(keymaps) == 0 {
+			out.Body.Reason = "kbd is not installed on this server (install the kbd / console-data package to enable keymap selection)"
+		}
 		return out, nil
 	})
 
@@ -209,7 +235,7 @@ func registerLocale(api huma.API) {
 			"already generated, returns 200 immediately.",
 		Tags:     []string{tagSystem},
 		Metadata: op("write"),
-		Errors:   append(writeErrors, 501),
+		Errors:   []int{400, 401, 403, 500, 501},
 	}, func(ctx context.Context, in *GenerateLocaleInput) (*oscmd.StatusOutput, error) {
 		locale := strings.TrimSpace(in.Body.Locale)
 		if locale == "" {
@@ -263,9 +289,16 @@ func enableLocaleGen(path, locale string) error {
 	if !found {
 		return huma.Error400BadRequest("locale not available for generation: " + locale)
 	}
-	if err := os.WriteFile(path, []byte(newContent), 0644); err != nil {
+	// Write atomically: a crash mid-write would leave /etc/locale.gen truncated
+	// and break every subsequent locale-gen on the host.
+	tmp := path + ".nadir.tmp"
+	if err := os.WriteFile(tmp, []byte(newContent), 0644); err != nil {
 		return huma.Error500InternalServerError("writing locale.gen failed", err)
 	}
+	if err := os.Rename(tmp, path); err != nil {
+		os.Remove(tmp)
+		return huma.Error500InternalServerError("replacing locale.gen failed", err)
+	}
 	if _, err := oscmd.Run("locale-gen"); err != nil {
 		return huma.Error500InternalServerError("locale-gen failed", err)
 	}

internal/modules/system/system_handler_test.go

@@ -142,7 +142,7 @@ func TestSystemHandlers(t *testing.T) {
 	// 4. Test GET & POST /api/system/locale
 	oscmd.SetMock("localectl", func(args []string) oscmd.MockCommand {
 		if reflect.DeepEqual(args, []string{"status"}) {
-			statusOut := "   System Locale: LANG=it_IT.UTF-8\n       VC Keymap: it\n      X11 Layout: it\n"
+			statusOut := "   System Locale: LANG=it_IT.UTF-8\n                  LANGUAGE=en_US:\n       VC Keymap: it\n      X11 Layout: it\n"
 			return oscmd.MockCommand{Stdout: statusOut, ExitCode: 0}
 		}
 		if reflect.DeepEqual(args, []string{"list-locales"}) {
@@ -151,6 +151,9 @@ func TestSystemHandlers(t *testing.T) {
 		if reflect.DeepEqual(args, []string{"set-locale", "LANG=it_IT.UTF-8"}) {
 			return oscmd.MockCommand{ExitCode: 0}
 		}
+		if reflect.DeepEqual(args, []string{"set-locale", "LANG=it_IT.UTF-8", "LANGUAGE=en_US:"}) {
+			return oscmd.MockCommand{ExitCode: 0}
+		}
 		if reflect.DeepEqual(args, []string{"list-keymaps"}) {
 			return oscmd.MockCommand{Stdout: "it\nus\n", ExitCode: 0}
 		}
@@ -168,7 +171,7 @@ func TestSystemHandlers(t *testing.T) {
 	if err := json.Unmarshal(resp.Body.Bytes(), &localeRes.Body); err != nil {
 		t.Fatal(err)
 	}
-	if localeRes.Body.Lang != "it_IT.UTF-8" || localeRes.Body.VCKeymap != "it" {
+	if localeRes.Body.Lang != "it_IT.UTF-8" || localeRes.Body.Language != "en_US:" || localeRes.Body.VCKeymap != "it" {
 		t.Errorf("got locale status: %+v", localeRes.Body)
 	}
 
@@ -186,6 +189,17 @@ func TestSystemHandlers(t *testing.T) {
 		t.Errorf("set locale: got %d, want %d", resp.Code, http.StatusOK)
 	}
 
+	resp = api.Post("/api/system/locale", struct {
+		Lang     string `json:"lang"`
+		Language string `json:"language"`
+	}{
+		Lang:     "it_IT.UTF-8",
+		Language: "en_US:",
+	})
+	if resp.Code != http.StatusOK {
+		t.Errorf("set locale with language: got %d, want %d", resp.Code, http.StatusOK)
+	}
+
 	resp = api.Get("/api/system/keymaps")
 	if resp.Code != http.StatusOK {
 		t.Errorf("list keymaps: got %d, want %d", resp.Code, http.StatusOK)